The Zune music service never really made a great impact in the marketplace, but it certainly attracted a faithful following among diehard fans who purchased Zune-branded players. However, more recently, it has been introduced to a much larger number of users thanks to its availability on Windows Phone 7 and Xbox 360 in various regions.

The key to the service’s admittedly modest success so far, has been the Zune Music Pass, a DRM-protected music subscription service which allows users to download and stream as much music as they like for as long as they maintain their monthly subscription. In the US, subscribers are also gifted ten DRM-free songs per month, which can be retained even if the subscription is cancelled.

For Zune Music Pass users, this is a pretty sweet deal, and it’s been made that little bit sweeter by the facility to associate numerous devices with the Pass, so that users can enjoy their music at home or at work, on PCs, phones, Xboxes or Zune players.

So today, Zune users may be slightly irked to hear that from 13 September 2011, the company is reducing the number of devices to which Zune Music Pass content can be downloaded, from the current level of six (3 PCs and 3 Windows Phones) to just four (at least one PC, plus any combination of 3 PCs or Windows Phones).

No reason has been given for the change, and the email makes it clear that subscribers’ continued use of Zune Music Pass beyond 13 September will implicitly confirm their agreement to the new arrangements.

Interestingly, the email excludes any mention of Zune hardware, so it may be that these changes do not affect users in the US or Canada (these are the only markets where Zune player hardware has been made officially available by Microsoft).

Update: As noted in comments below, and reported at LiveSide.net, it seems that these changes will affect Zune Music Pass subscribers in Europe only. Thanks to Omen1393 for pointing this out.